1. Field of the Invention
The present invention relates to a fuel injection valve provided with a plate having a plurality of injection holes at an injection port of a valve body thereof.
2. Description of Related Art
Recently, many high performance engines have been proposed that have a plurality of intake ports (a plurality of intake valves) in each of the cylinders. For example, as disclosed in JP-U-H.3-63763(refer to FIGS. 4 and 5), a fuel injection valve to be installed in an intake manifold of the engine is provided with a plate 13 having a plurality of injection holes 12a and 12b at an injection port of a valve body 11. Inclination angles (injection direction) of the respective holes 12a and 12b are so formed that fuel from the holes 12a and 12b may be injected toward the intake ports 14a and 14b on target, respectively. a group A of the injection holes 12a through which fuel is injected toward the intake port 14a and a group B of the injection holes 12b through which fuel is injected toward the intake port 14b. As the respective hole diameters of the injection holes 12a and 12b are same, a fuel flow amount distribution rate of the group A to the group B is considered adjustable by respective piece numbers of the injection holes 12a and 12b to be classified into the respective groups A and B.
In the fuel injection valve 10 mentioned above, the three group A injection holes 12a are arranged on a straight line. In the case of such a straight-line arrangement, the fuel flow amounts in the respective injection holes 12a are not identical, even if the hole diameters are the same. The reason is that, as highly pressurized fuel flows onto the plate 13 so as to swirl in a circular direction from an outer circumference gap of a needle valve (not shown), a flow speed of the fuel becomes variable along a radial direction on the plate 13.
Further, in a region of the plate 13 near the outer circumference thereof, the fuel flows downward obliquely from the outer circumference gap of the needle valve. An inflow angle of the fuel downward obliquely flowed to the plate 13 becomes smaller at a position nearer to the inside thereof. Therefore, respective flow amounts of the three injection holes 12a arranged on a straight line are different from each other, as the flow speeds and the inflow angles of the fuel to be flowed into the respective three injection holes 12a are different. As a result, it is very difficult to accurately adjust the fuel flow amount distribution rate of the group A injection holes to the group B injection holes only by the numbers of injection holes 12a and 12b.
Further, an injection valve is known, as shown in FIG. 6, in which a plate 15 is provided with same hole diameter injection holes 1 to 5 arranged on a circumference of a circle. The respective injection holes 1 to 5 are formed obliquely at an inclination angle (in an injection direction) so that the fuel from the respective injection holes 1 to 5 may be injected toward the respective intake ports on target. By arranging the injection holes 1 to 5 on the circumference of the circle, the respective flow speeds and the respective inflow angles of the fuel flowed into the respective injection holes 1 to 5 becomes identical. However, as shown in FIG. 7, the fuel flow amounts in the respective injection holes 1 to 5 are different from each other as the inclination angles of the respective injection holes 1 to 5 are different even if the hole diameters thereof are the same.
Next, with reference to FIG. 8, a reason why the respective different inclination angles of the injection holes 1 to 5 cause different fuel flow amounts is described. When the fuel, flowed onto the plate 15 from a gap between a needle valve and a valve body, flows in the respective injection holes 1 to 5, a contraction of the fuel flow takes place. As the contraction takes place based on an inertial force due to a fuel flow direction conversion, the contraction becomes larger in the injection holes 1 to 5 having the larger inclination angle. Therefore, as shown in FIG. 7, the fuel injection amount is smaller in the injection holes 1 to 5 having the larger inclination angle. As mentioned above, even if the same diameter injection holes 1 to 5 are arranged on the circumference of the circle, the fuel flow amounts in the respective injection holes 1 to 5 differ due to the difference of the respective inclination angles of the injection holes 1 to 5. As a result, the fuel flow amount distribution rate on target of one injection hole to another injection hole among the injection holes 1 to 5 or of the group A injection holes to the group B injection holes is hardly secured. FIG. 7 shows a relationship between an inclination angle of the injection hole and a flow amount rate, when the flow amount of the injection hole 5 having the inclination angle of 30.degree. is referenced as 100.
Though the fuel flow amount distribution rate may be adjusted by changing the respective hole diameters of the infection holes 1 to 5, such a change causes a higher manufacturing cost for fabricating the injection holes 1 to 5.